Motorola HT Series Service Manual page 39

7KHRU\ RI 2SHUDWLRQ /RZ %DQG 5HFHLYHU
Antenna
Lowpass
RFJack Filter
 5HFHLYHU )URQW(QG
7KH 5) VLJQDO UHFHLYHG E\ WKH DQWHQQD LV URXWHG WKURXJK WKH WUDQVPLWWHU ORZSDVV ILOWHU DQG DQWHQQD
VZLWFK 7KHVH FLUFXLWV DUH GHVFULEHG LQ WKH WUDQVPLWWHU VHFWLRQ7KH VLJQDO QH[W SDVVHV WKURXJK D
KLJKSDVV ILOWHU FRQVLVWLQJ RI / / & & DQG & 7KLV ILOWHU VHUYHV WR UHMHFW EHORZ
EDQG VLJQDOV DQG KDV D  G% FRUQHU IUHTXHQF\ RI  0+]
7KH RXWSXW RI WKH KLJKSDVV ILOWHU LV FRQQHFWHG WR DQ 5) DPS FRQVLVWLQJ RI 4 DQG DVVRFLDWHG
ELDVLQJ FRPSRQHQWV 7KLV LV D %-7 DPSOLILHU SRZHUHG RII  YROWV DQG KDV  G% RI JDLQ 7KH DPSOLILHU
GULYHV D ORZSDVV ILOWHU FRQVLVWLQJ RI / / / & & & & DQG & 7KLV ILOWHU
LV D SROH ]HUR GHVLJQ WKDW ILOWHUV RII KDUPRQLF FRPSRQHQWV IURP WKH 5) DPS 7KH  G% FRUQHU RI WKLV
ILOWHU LV DW  0+]
7KH RXWSXW RI WKH ORZSDVV ILOWHU LV FRQQHFWHG WR WKH SDVVLYH GRXEOH EDODQFHG PL[HU FRQVLVWLQJ RI
FRPSRQHQWV 7 7 DQG ' $IWHU PL[LQJ ZLWK WKH ILUVW ORFDO RVFLOODWRU XSFRQYHUWHG WR D
  0+] ,) VLJQDO
7KH ,) VLJQDO FRPLQJ RXW RI WKH PL[HU LV WUDQVIHUUHG WR WKH FU\VWDO ILOWHU )/ WKURXJK D UHVLVWRU SDG
5 5 DQG 5 DQG D GLSOH[HU & DQG /  0DWFKLQJ WR WKH LQSXW RI WKH FU\VWDO ILOWHU LV
SURYLGHG E\ / / & DQG & 7KH  SROH FU\VWDO ILOWHU SURYLGHV WKH QHFHVVDU\ VHOHFWLYLW\
DQG LQWHUPRGXODWLRQ SURWHFWLRQ
Antenna
Highpass
Switch
Filter
First LO
from FGU
Recovered Audio
17.0 MHz
Reference Clock
)LJXUH  /RZ %DQG 5HFHLYHU %ORFN 'LDJUDP
RF Lowpass
Amp Filter
Squelch
IF IC U303
RSSI
IF
Crystal
Mixer
Amp
Filter
AGC
Processing
Demodulator
Synthesizer
SPI Bus

Second
LO VCO